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    Re: Leap seconds at Big Ben.
    From: Lu Abel
    Date: 2008 Dec 31, 15:08 -0800

    George, adjusting Big Ben was even carried on the BBC World News
    program, which is broadcast in the US on many of our Public Broadcasting
    (non-profit, no advertising) stations.  Gaza, Iraq, Big Ben (in that
    order).  Just heard the broadcast, complete with an interview with the
    bloke that is adding (or subtracting) the pennies.   Sounds like his
    goal was to slightly modify the pendulum rate, thereby slowing Big Ben
    over a period of time (again, not exactly specified) so that it will
    strike midnight one second later than it normally would.
    What I find puzzling, though, is that a pendulum's rate is controlled by
    its length and not its weight.  So the only thing I can guess is that
    the pennies added or subtracted move the center of the pendulum's mass
    slightly upward or downward.
    Cheers, and Happy New Year (one second late!)
    Lu Abel
    George Huxtable wrote:
    > A bit more information about leap seconds, for anyone who happens to be
    > interested.
    > The chimes of Big Ben, from London, ring in the New Year, via radio and TV,
    > all over Britain, and over much of the Western World that has so far escaped
    > the dominion of the USA. The clock dates from nearly 150 years ago, the work
    > of Nicholas Denison.
    > Those responsible for the mechanism have the task of introducing a leap
    > second, for which the mechanism was never designed. It wouldn't do to have
    > the bells ring out a second before the due moment of New Year. My wife Joan,
    > who takes an interest in such matters as her birthday is on New Year's Day,
    > heard a news item on the radio about how the job is done, and has passed the
    > information on.
    > There is no seconds-hand on the clock, but presumably there must be an
    > internal cam-wheel, turning as a seconds-hand would, to trigger the strike.
    > The pendulum, nearly 4 metres long beats at 2-second intervals, a cycle
    > taking 4 seconds, so that wheel would step at 2-second intervals.
    > It wasn't made clear exactly how long before the moment of New Year the
    > adjustment process for the leap-second commences, but the job has to be done
    > gradually, as the required step-change is impossible. To adjust the rate,
    > weights are added or subtracted from a tray that's attached to the pendulum.
    > Traditionally, these have been (old) pennies, copper coins valued at a bit
    > less han half of one (new) pence. This allows the clock to run a bit more
    > slowly as the leap-second moment is approached, so that at New Year, it
    > strikes correctly, allowing for the leap-second, and the rate of going can
    > then be returned to normal. That must mean that during the adjustment
    > period, the clock must be increasingly slow on UT, by up to ! second.
    > Presumably, that will affect the strikings (at the quarter-hours) that
    > precede midnight.
    > A happy New Year to all,
    > from George.
    > contact George Huxtable, at  george@hux.me.uk
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > >
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